Stem Cell Factor (SCF, also known as mast cell growth factor), is the ligand for KIT, a receptor tyrosine kinase. The goal of this proposal is to determine the role of the SCF-KIT signaling pathway in mastocytosis and cutaneous inflammation. Mastocytosis occurring sporadically in adults is caused by somatic mutations affecting the primary sequence of KIT and causing constitutive activation of KIT and its downstream transducing molecule PI3-K, which causes phosphorylation of AKT. Familial and most pediatric cases of mastocytosis cases show normal KIT protein coding sequence but have phosphorylated AKT in lesional mast cells. Our first hypothesis is that familial and sporadic pediatric mastocytosis are caused by mutations affecting the SCF-KIT signaling pathway, or pathways convergent with it at or above AKT. Human epidermal keratincytes produce SCF, and dermal injection of SCF causes inflammation. Trangenic mice which express epidermal SCF, like humans, show an exaggerated ear swelling response to allergic and irritant contactants. Our second hypothesis is that SCF-KIT signaling plays an active role in the cutaneous inflammatory response. Our specific aims are: 1. To determine the mechanism(s) of oncogenesis in c-KIT mutation negative pediatric mastocytosis, mRNA from lesional mast cells will be RT-PCR amplified and sequenced to detect mutations in genes encoding molecules which may affect AKT phosphorylation including AKT, PTEN, Lyn and PI3-K. Since loss of PTEN could result in increased PI3-K signaling, lesional mast cell DNAk will also be tested for loss of heterozygosity in region 10q23 by microsatellite analysis. The functional effects of mutations or gene loss will be determined in cultured bone marrow derived mast cells an mast cell lines by retroviral expression of mutant activating or dominant negative proteins, or by anti-sense suppression. 2. To determine the genetic basis of familial mastocytosis, two separate kindreds with dominantly inherited mastocytosis will be tested for linkage to genes known to affect the KIT-P13-K signaling pathway using microsatellite analysis. If necessary, a genome-wide screen of affected and genetically relevant unaffected individuals will be performed using loci at 10 cM intervals followed by positional cloning and gene identification. 3. To test the hypothesis that SCF-KIT signaling is actively involved in the afferent, efferent, or both arms of the cutaneous immune response, we will use adoptive transfer of immune lymphocytes, KIT blocking antibodies, and small molecule inhibitors of KIT in a series of DNFGB sensitivity studies in normal mice, and in a proven transgenic model of SCF-KIT mediated cutaneous inflammation. These studies will determine specific contributions of SCF-KIT signaling to contact dermatitis, an provide support for the hypothesis that inhibitors of KIT may be novel therapeutic agents for human cutaneous inflammation.